Gentamicin Dosing for an 80kg Patient with UTI
For an 80kg patient with a urinary tract infection, the recommended gentamicin dosage is 5-7 mg/kg/day as a single daily dose, which equals 400-560 mg once daily. 1
Dosing Considerations
Standard Dosing for UTI
- For urinary tract infections specifically, aminoglycoside monotherapy is appropriate 1
- The FDA-approved dosing for adults with serious infections and normal renal function is 3 mg/kg/day divided into three equal doses every 8 hours 2
- However, for UTIs specifically, higher doses of 5-7 mg/kg/day as a single daily dose are recommended 1
- For this 80kg patient:
- At 5 mg/kg: 400 mg once daily
- At 7 mg/kg: 560 mg once daily
Duration of Treatment
- For complicated UTIs, the suggested treatment duration is 5-7 days 1
- The usual duration for gentamicin treatment is generally 7-10 days 2
Administration Method
- For intravenous administration, gentamicin should be diluted in 50-200 mL of sterile isotonic saline or 5% dextrose solution 2
- The solution should be infused over 30-60 minutes 3
- Standard infusion concentration is 480mg in 100mL at a rate of 200mL/hour for a 30-minute infusion 3
Monitoring Requirements
- Target peak levels: 4-6 mcg/mL (measured 30-60 minutes after administration) 2
- Avoid prolonged levels above 12 mcg/mL 2
- Target trough levels: <2 mcg/mL (measured just prior to next dose) 2
- For once-daily dosing, trough levels should be <1 mcg/mL 3
Special Considerations
Lean Body Mass Adjustment
- The FDA label specifically states that dosing in obese patients should be based on lean body mass rather than total body weight 2
- If the patient has significant obesity, the dosage should be adjusted accordingly
Renal Function
- Renal function must be assessed before initiating therapy
- Dosage should be reduced in patients with impaired renal function 2
- For patients with normal renal function, once-daily dosing of 240mg has been shown to achieve adequate peak concentrations without requiring monitoring for short courses (≤3 days) 4
Evidence for Once-Daily Dosing in UTI
- Research has demonstrated that a single daily dose of gentamicin (160 mg) eliminated bacteriuria in all patients with lower UTI 5
- Once-daily dosing achieves higher peak concentrations which enhances the bactericidal effect while minimizing toxicity 4
Cautions
- Monitor renal function throughout therapy, as gentamicin can cause nephrotoxicity
- Extended treatment beyond 10 days increases risk of toxicity; monitoring of renal, auditory, and vestibular functions is recommended in such cases 2
- Avoid physical premixing with other drugs; administer gentamicin separately 2
By following these dosing guidelines, the 80kg patient with UTI should receive effective antimicrobial therapy while minimizing the risk of adverse effects.